1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of handling a device-to-device operation and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Device-to-device (D2D) communication may be realized, after an initialization (e.g., connection establishment and/or peer discovery) is performed (e.g., assisted by an eNB). Then, a group of UEs may communicate (e.g., transmitting and/or receiving packets) with each other directly according to the D2D communication, and the eNB does not need to forward the packets transmitted between the communication devices. According to the D2D communication, the UEs may communicate with each other via UL resources (e.g., UL subframes configured by the eNB). In general, the D2D communication may also be seen as a D2D service (i.e., proximity service (ProSe)). In addition, a D2D subframe, D2D transmission, D2D communication and D2D discovery can be termed as a sidelink subframe, sidelink transmission, sidelink communication and sidelink discovery, respectively.
A UE may perform a D2D operation and a device-to-cellular (D2C) operation at the same time (e.g., in the same time interval). The situation may be that the UE is in a coverage area of a cell of the eNB, and the D2D communication and the D2C communication are both supported by the cell. However, the D2D operation may be affected by the D2C operation. For example, the UE may not know how to transmit a hybrid automatic repeat request (HARQ) feedback in a UL subframe according to a predetermined rule of the D2C communication, when the UL subframe is scheduled for the D2D operation. The problem may occur in a time-division duplexing (TDD) mode or a frequency-division duplexing (FDD) mode of the D2C communication. The problem may also occur when other transmission (e.g., UL control information and/or UL data) for the D2C communication is to be performed. The D2D operation and the D2C operation may not be performed regularly.
Thus, the collision between the D2D operation and the D2C operation is an important problem to be solved.